The invention relates to an extension assembly for use with a tube expander of the type which is inserted into a tube for expanding the tube into rigid engagement with structural supports. A bank of such tubes may, for example, form a heat exchanger, the construction of which requires each tube to be rigidly expanded into a sheet which supports the tubes.
Tube expanders typically require the ability to provide substantial rotational force to an expanding head while the expanding head simultaneously provides radially outward pressure so that the metal tubes can be sufficiently deformed to provide rigid engagement. The support sheets or frame work of sheets into which the tube must be expanded are typically at multiple distances along the length of the tube so that the expander must be inserted substantial distances into the tube. Where the entry end of the tube is not adjacent any other structure, straight rigid extensions can be used without difficulty. However, where the end of the tube is blocked so that a straight extension cannot be used, flexible extensions are required so that the tube expander can be inserted a sufficient distance into the tube while the flexible extension is bent for entry into the tube.
With prior art flexible extensions, difficulties arise, for example, where the tube expander is of the type which has rollers held in cages which rollers are pushed radially outward by an internal mandrel it is necessary to have one flexible mandrel extension inside a flexible tube extension. The forces which can be applied using continuously flexible tubing such as coiled spring tubing is limited and often not sufficient to provide adequate rotational force to provide the tube expansion and rigidity of engagement required. Problems of extender deformation result. Also problems of inadequately expanded tube engagement may result.
There is also a severe space constraint as the inside diameter of the tubes can be less than one-fourth of an inch (6.35 millimeters) in diameter. Thus, there is often insufficient room to provide universal joint connections with sufficient strength to ensure adequate torsional force applied to the expansion head or roller cage.